Scanner and calibration method used therein

ABSTRACT

A scanner and calibration method use therein. Setting first exposure duration and a second exposure duration for a transparency, wherein the first exposure duration is proportional to the second exposure duration. Scanning the transparency and a calibration area to produce a scan signal and a calibration signal, respectively, wherein the exposure duration for scanning the transparency is referred to as the first exposure duration, and the exposure duration for scanning the calibration area is referred to as the second exposure duration. Calculating a first gain coefficient according to the calibration signal. Calculating a second gain coefficient according to the first gain coefficient and a specific ratio of the first exposure duration to the second exposure duration, and finally, amplifying the scan signal by the second gain coefficient.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a calibration method, and moreparticularly to an effective calibration method used by a transparencyscanner.

2. Description of the Related Art

Currently, a plate scanner, to scan a transparency, may use a scanningmask. However, the transparency, including a positive film or a negativefilm, has a wider exposure margin than a non-transparent object due tothe film substrate, and requires longer exposure duration. Thus, whenscanning the transparency, the plate scanner must be calibrated withincreased exposure duration. Typically, there are two methods forcalibrating a scanner. The first calibration method results in excessiveexposure duration, easily causing a saturation of the scan signal. Thesecond calibration method places transparent tape above a calibrationarea. This method, however, has a complex design, higher manufacturingcost, and low precision.

FIG. 1 a is a block diagram of a conventional scanner. FIG. 1 b is aschematic figure of an object placed on the platen of the scanner ofFIG. 1 a. In FIG. 1 a and FIG. 1 b, a glass platen 120 is installedbetween a lamp 102 and a charge-coupled capture device 104, and has acalibration area 122 and a scanning area 124, and a transparency 126 isplaced on the scanning area 124.

When scanning the transparency 126, the calibration area 122 is alsoscanned according to the same exposure duration, to produce an analogscan signal SA and an analog calibration signal, respectively. A signalprocessing device 106 then converts the analog scan signal SA into adigital scan signal SD. The image processing device 110, then receivesthe digital scan signal DA, for related image processing.

To prevent data loss, however, the analog scan signal SA must beamplified by a gain coefficient before conversion, wherein the gaincoefficient is calculated by the calibration signal.

FIG. 2 is a curve of a scan signal of the scanner of FIG. 1 a. In FIG.2, a scan signal 22 is a signal output from the charge-coupled capturedevice 104, and a signal 24 is a product of the scan signal 22 and again coefficient. The amplitude of the scan signal 22 is between 0 toM1, and a range of a digital scan signal converted from the scan signal22 is between 0 to D1. Commonly, an ideal range of the digital scansignal is between 0 to D2, while D2 is the maximum digital value afterthe conversion. The maximum digital value, for example, of an 8 bitsignal processing device is 255 or near 255 calculated by 2⁸−1.

Thus, to obtain ideal digital signal range, the original scan signal 22,must be amplified into the signal 24 having an amplitude range between 0to M2 by the calibration signal before conversion.

The exposure duration of scan signal 22, however, is affected bydifferent film substrates. Hence, when using the same exposure durationto scan the calibration area and the transparency 126, according to therelated art, a suitable gain coefficient for amplifying the scan signal22 to be converted into the digital scan signal having the maximumdigital value D2 cannot be obtained.

Therefore, the present invention provides a calibration method using twodifferent exposure durations to obtain a suitable calibration signal anda scan signal, respectively. The scan signal is then calibratedaccording to the calibration signal thereby obtaining a digital scansignal having a maximum digital value.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for scanningand calibrating an object using two different exposure durations,thereby calculating a gain coefficient by a specific ratio to obtain adigital scan signal having a maximum digital value.

Another object of the present invention is to provide a scanner usingmultiple exposures of varying duration, thereby calculating a gaincoefficient based on a specific calibration to scan signal ratio withthe resulting analog scan signal, finally generating digital scan signalproviding an ideal calibration range after conversion.

For the purpose above, the present invention provides a calibrationmethod comprising the steps of setting a first exposure duration and asecond exposure duration according to a transparency, wherein the firstexposure duration is proportional to the second exposure duration,scanning the transparency and the calibration area to produce a scansignal and a calibration signal, respectively, wherein the exposureduration for scanning the transparency is referred to as the firstexposure duration, and the exposure duration for scanning thecalibration area is referred to as the second exposure duration,calculating a first gain coefficient according to the calibrationsignal, calculating a second gain coefficient according to the firstgain coefficient and a specific ratio of the first exposure duration tothe second exposure duration; and amplifying the scan signal by thesecond gain coefficient.

Additionally, the present invention provides a scanner having an opticalimage capture system, an optical sensing capture device and a signalprocessing device. The image capture system scans a transparency forfirst exposure duration to produce a scan signal, and scans acalibration area for second exposure duration to produce a calibrationsignal. The signal processing device calculates a first gain coefficientaccording to the calibration signal, calculates a second gaincoefficient according to the first gain and a specific ratio, andamplifies and converts the scan signal into a digital signal accordingto the second gain coefficient.

Furthermore, the present invention provides another calibration methodcomprising the steps of scanning a transparency according to a firstexposure duration to produce various image data, converting the imagedata into various digital data, and analyzing the digital data to obtaina maximum value of the digital data, calculating a gain coefficientaccording to the maximum value, wherein the gain coefficient is amaximum gain value for amplifying the image data to be converted,calculating a second exposure duration by a product of the gaincoefficient and the first exposure duration, and scanning thetransparency with the second exposure duration to obtain an ideal scansignal.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description in conjunction with the examples andreferences made to the accompanying drawings, wherein:

FIG. 1 a is a block diagram of a scanner according to the prior art;

FIG. 1 b is a schematic figure of an object placed on the glass platenof the scanner of FIG. 1 a;

FIG. 2 is a curve of a scan signal of the scanner of FIG. 1 a;

FIG. 3 is a flowchart of a calibration method of a first embodiment ofthe present invention;

FIG. 4 a is a block diagram of the first embodiment of a scanner usingthe calibration method of FIG. 3;

FIG. 4 b is schematic figure of an object placed on a glass platen ofthe scanner of FIG. 4 a;

FIG. 5 is a block diagram of a second embodiment of the scanner usingthe calibration method of FIG. 3;

FIG. 6 shows a flowchart of a calibration method of the secondembodiment.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a method for scanningand calibrating an object using two different exposure durations,thereby calculating a gain coefficient by a specific ratio to obtain adigital scan signal having a maximum digital value.

First Embodiment

FIG. 3 is a flowchart of a calibration method of the first embodiment ofthe present invention. The calibration method calibrates the scan signalof a scanner having an optical sensing capture device by linearlyadjusting exposure duration.

Step S302 first sets a scanning duration and a calibrating duration ofan optical sensing capture device for a transparency, wherein thescanning duration is proportional to the calibrating duration.

Step S304 follows and scans the transparency and a calibration area toproduce a scan signal and a calibration signal, respectively, whereinthe exposure duration for scanning the transparency is referred to asthe scanning duration, and the exposure duration for scanning thecalibration area is referred to as the calibrating duration.

Step S306 follows and calculates a first gain coefficient according tothe calibration signal, wherein the first gain coefficient is a maximumgain coefficient for amplifying the scan signal to be converted into amaximum digital signal.

Step S308 follows and calculates a second gain coefficient according tothe first gain coefficient and a specific ratio of the first exposureduration to the second exposure duration.

The above steps are suitable for scanning a positive film or a highlytransmissive object. To scan a negative film or a low transmissiveobject, however, increased exposure duration is required.

Step S310 follows and determines whether the second gain coefficient isless than one. If the result from step S310 is positive, step S312follows and sets the second gain coefficient equal to one, and thenamplifies the scan signal by the second gain coefficient to maintain thescan signal. If the result is negative, step 314 follows and amplifiesthe scan signal by the second gain coefficient directly.

FIG. 4 a is a block diagram of the first embodiment of a scanner usingthe calibration method of FIG. 3. FIG. 4 b is a schematic figure of anobject placed on a glass platen of the scanner of FIG. 4 a. In FIG. 4 aand FIG. 4 b, a scanner 400 comprises an optical image capture system410, a signal processing device 420, an image processing device 430 anda setting device 432. The optical image capture system 410 comprises alamp 412 and a charge-coupled capture device 414, and the signalprocessing device 420 comprises a gain unit 422, an A/D converter 424and a control unit 426. A glass platen 440, which is installed betweenthe lamp 412 and the charge-coupled capture device 414, has acalibration area 442 and a scanning area 444 on which the transparency446 is placed.

Hence, a scanning duration Ts and a calibrating duration Tc of thesetting device 432 can be set manually according to the transparency446. The lamp 412 and the charge-coupled capture device 414 scan thetransparency 446 according to the scanning duration Ts, and scan thecalibration area 442 according to the calibrating duration Tc, therebyobtaining a scan signal As and a calibration signal Ac, respectively.

The A/D converter 424 converts the scan signal into a digital scansignal Dc according to the scan signal Ac. In addition, the control 426calculates a gain coefficient Gc according to the digital scan signalDc, wherein the gain coefficient Gc is a maximum gain coefficient foramplifying the scan signal Ac to be converted into the digital scansignal Dc having a maximum digital value. The maximum digital value, forexample, of an 8 bit A/D converter is 255 or near 255 calculated by2⁸−1.

Next, the control unit 426 calculates a gain coefficient Gs according tothe gain coefficient Gc and a specific ratio of the scanning duration Tsto the calibrating duration Tc, wherein the coefficient Gs is calculatedby Gs=Gc×Tc/Ts.

The gain unit 422 amplifies the scan signal As according to the gaincoefficient Gs. The A/D converter 424 then converts the scan signal Asinto a digital scan signal Ds and, according to the digital scan signalDs, the image processing device 430 performs related image processing.

Additionally, when the coefficient Gs is less than one, the control unit426'sets the coefficient Gs equal to one thereby transmitting the scansignal As to the A/D converter 424 directly.

The transparency 446 is either a positive film or a negative film. Forexample, when scanning a positive film, a calibrating duration Tc and ascanning duration Ts by the setting device 432 can be set manually,wherein the calibrating duration Tc is equal to one and the scanningduration Ts is equal to twice the calibrating duration Tc or two. Theamplitude of the calibration signal Ac then equals half the amplitude ofthe scan signal As. If the gain coefficient Gc is equal to two,according to the gain coefficient Gc and a specific ratio of thescanning duration Ts to the calibrating duration Tc, the control unit426 obtains the gain coefficient Gs to be equal to two by the followingequations:Dc=Ac×Gc, Ac=Tc×E×R;Ds=As×Gs, As=Ts×E×R;

Wherein, E is luminous intensity, R is a response coefficient of thecharge-coupled capture device 414. Following above equations, thedigital value Dc is equal to the digital value Ds, while Ts=2Tc andGc=2Gs.

Hence, the scan signal will not saturate the object during calibrationand the digital scan signal will have an ideal digital range after theA/D conversion according to the calibration method of the presentinvention.

A negative film has wider exposure margin than a positive film due tothe different film substrate. Hence, to scan the negative film, thescanner 400, requires longer exposure duration. Commonly, the exposureduration of a negative film is 3 to 4 times the value of a positivefilm. The film substrate is an attenuation factor of the light source.Hence, to obtain the ideal signal, shorter exposure duration requiresmore calibration, and, comparatively, longer exposure duration requiresless or no calibration. Thus, the gain coefficient Gs of the settingdevice 432 is be set as equal to one when scanning the negative film.

Second Embodiment

FIG. 5 is a block diagram of a second embodiment of the scanner usingthe calibration method of FIG. 3. The scanner 500 comprises an opticalimage capture system 510, a signal processing device 520, an imageprocessing device 530 and a setting device 532. The optical imagecapture system 510 comprises a lamp 512 and a charge-coupled capturedevice 514, and the signal processing device 520 comprises a gain unit522, an A/D converter 524 and a control unit 526. In this embodiment,the scanner 500 has two scan modes, one of which is chosen for scanninga positive film and the other for scanning a negative film.

When the positive film scan mode is chosen, the lamp 512 and thecharge-coupled capture device 514 scan a transparency with scanningduration Ts1 and, scan a calibration area with a calibration durationTc1 thereby producing a scan signal As1 and a calibration signal Ac1,respectively, wherein the scan signal As1 and the calibration signal Ac1are predetermined and stored in the setting device 532.

The A/D converter 524 receives and converts the scan signal Ac1 into adigital scan signal Dc1. The control 526 calculates a gain coefficientGc1 according to the digital scan signal Dc1, wherein the gaincoefficient Gc1 is a maximum gain coefficient for amplifying the scansignal to be converted into the digital scan signal having a maximumdigital value. The maximum digital value, for example, of an 8 bit A/Dconverter is 255 or near 255 calculated by 2⁸−1.

Next, the control unit 526 calculates a gain coefficient Gs1 accordingto the gain coefficient Gc1 and a specific ratio of the scanningduration Ts1 to the calibrating duration Tc1, wherein the coefficientGs1 is calculated by G_(S1)=G_(C1)×T_(c1)/T_(S1).

The gain unit 522 amplifies the scan signal As1 by the gain coefficientGs1. The A/D converter 524 then converts the scan signal As1 into adigital scan signal Ds1. Thus, the image processing device 530 performsrelated image processing according to digital scan signal Ds1.

When the negative film scan mode is chosen, the lamp 512 and thecharge-coupled capture device 514 scan a transparency according to ascanning duration Ts2, and scan a calibration area according to acalibration duration Tc2 thereby producing a scan signal As2 and acalibration signal Ac2, respectively, wherein the scan signal As2 andthe calibration signal Ac2 are predetermined and stored in the settingdevice 532.

A negative film has wider exposure margin than a positive film due tothe different film substrate. Hence, to scan the negative film, thescanner 500 requires longer exposure duration. Commonly, the exposureduration of a negative film is 3 to 4 times the value of the positivefilm. The film substrate is an attenuation factor of a light source.Hence, to obtain the ideal signal, shorter exposure duration requiresmore calibration, and comparatively, longer exposure duration requiresless or no calibration. Thus, the gain coefficient Gs2 of the settingdevice 532 would be set equal to one when scanning negative film.

Additionally, to obtain an ideal digital range after the A/D conversion,the scan signal must be calibrated as long as possible before conversionthereby increasing the exposure duration. Hence, the present inventionfurther provides a method for increasing the exposure duration.

FIG. 6 shows a flowchart of a calibration method of the secondembodiment. Step S602 first rapidly scans a transparency to producevarious image data with exposure duration T1. The exposure duration T1must be short enough to prevent the various digital data to be convertedfrom the image data from exceeding a maximum value. Step S604 followsand converts the image data into digital data, thereby analyzing theimage data to obtain a maximum digital value M. Step S606 follows andcalculates a gain coefficient C according the maximum digital value M,wherein the gain coefficient C is a maximum gain coefficient foramplifying the image data to be converted into digital data having themaximum digital value M. The maximum digital value, for example, of an 8bit A/D converter is 255 near 255 calculated by 2⁸−1, and a gaincoefficient C could be calculated by the following equation:C=255/M

Hence, the image data, to be converted, is amplified with the gaincoefficient C and can obtain the maximum digital value M.

Step S608 follows and calculates an exposure duration T2 by the productof the gain coefficient C and the exposure duration T1, and finally,step S610 follows and scans the transparency with the exposure durationT2 to obtain an ideal scan signal.

Therefore, a calibration method and a scanner with the calibrationmethod of the present invention can calibrate and scan the transparencywith two different exposure durations, and calculate a gain coefficientbased on a specific calibration to scan signal ratio with the resultinganalog signal. Hence, the resulting signal, with any exposure duration,will not cause saturation during calibration, and can obtain an idealdigital signal range after conversion.

Finally, while the invention has been described by way of example and interms of the above, it is to be understood that the invention is notlimited to the disclosed embodiments. On the contrary, it is intended tocover various modifications and similar arrangements as would beapparent to those skilled in the art. Therefore, the scope of theappended claims should be accorded the broadest interpretation so as toencompass all such modifications and similar arrangements.

1-21. (canceled)
 22. A calibration method for a scanner, comprising thefollowing steps: scanning a transparency according to a first exposureduration to obtain various image data; converting the image data intovarious digital data, and analyzing the digital data to obtain a maximumdigital value; calculating a gain coefficient according to the maximumdigital value, wherein the gain coefficient is a maximum gaincoefficient for amplifying the image data to be converted into thedigital data having the maximum digital value calculating a secondexposure duration by the product of the gain coefficient and the firstexposure duration; and scanning the transparency by the second exposureduration, to obtain an ideal scan signal.
 23. The calibration method asclaimed in claim 22, wherein the maximum digital value is
 255. 24. Thecalibration method as claimed in claim 21, the transparency is apositive film or a negative film.